SPECTROELECTROCHEMICAL INVESTIGATIONS OF STOICHIOMETRY AND OXIDATION-REDUCTION POTENTIALS OF CYTOCHROME-C OXIDASE COMPONENTS IN PRESENCE OF CARBON-MONOXIDE - INVISIBLE COPPER

Spectroelectrochemical studies are presented for the CO complex of isolated, purified cytochrome c oxidase (EC 1.9.3.1) in solutions saturated with CO. A stoichiometry of 3 equivalents/oxidase CO complex molecule is indicated. Formal reduction potentials (E.degree.'') of the 2 Cu and 1 heme component at pH 7.0 were obtained using quantitative absorbance-charge titrations in the absence and presence of cytochrome c, and using a Nernstian Minnaert plot in the presence of cytochrome c. Analysis of the absorbance-charge curves from these titrations gave an indirect determination of the high potential, invisible Cu component. The Cu potentials in the CO complex were relatively unchanged with respect to those of the native enzyme. The E.degree.'' values obtained were: high potential (invisible) Cu (340 .+-. 20 mV (NHE [normal H electrode]), low potential Cu (190 .+-. 20 mV), and low potential heme (250 .+-. 10 mV).